Electronic piano



June 23, 1970 M. R. HARRIS ELECTRONIC PIANO 3 sh ets-sheet 1 Filed Jan. 19, 1967 IFSUSTAIN CKT;

I I l 8 OUTPUT 'INVENTOR MICHAEL HARRIS SMALL. R

ATTORNEYS June 23, 1970' M. R. HARRI 3 ,516,321

ELECTRONIC PIANO Filed Jan. 19, 1967 5 Sheets-Sheet 2 +llv.

:IGDV (-Vg) I INVENTOR MICHAELR. HARRIS 3| 3o 33 @5- GATE June 23, 1970 M. R. HARRIS ELECTRONIC PIANQ 5 shee ts-eshe v 5 TO FILTER HEADER Filed Jan. 19 196.7- 116.6

IM L5 v (UNDAMPED) INVEIQTOR- MICHAEL R. HARRIS ATTORNEYS United States Patent Ohio Filed Jan. 19, 1967, Ser. No. 610,423 Int. Cl. Gh 1/02 US. Cl. 84--1.13 12 Claims ABSTRACT OF THE DISCLOSURE An electronic piano in which a control voltage proportional to impact on or velocity of a key is produced in terms of decay of control voltage across a control or timing capacitor while a key operated switch arm moves from a first to a second contact, and in which the voltage is sampled via an isolating diode or transistor at the second contact and stored in an RC sustain circuit, the sustain voltage of which then decays and in decaying controls a tone envelope to simulate a piano key. Devices are provided for effecting damping on release of the key, and to disable damping in response to a pedal operation, and to provide double rate decay of voltage of the control or timing capacitor and of the sustain circuit voltage. The fact that the decay time of sustain voltage is slow and that decay of control voltage is rapid enables the diode or transistor toperform its isolating function.

BACKGROUND OF THE INVENTION This invention relates generally to electronic pianos and more particularly to electrical tone generating systems having facility for producing touch sensitive tones, which decay slowly while a key is held depressed, which decay rapidly when a struck key is released, and which can be caused to decay slowly by actuating of a damping pedal when the key is released.

Electronic pianos exist in the prior art, as in U.S. patents as follows: Markowitz, 3,248,470; Kerkhof, 2,482,- 548; Hammond, 2,126,464. The Markowitz patent relates to a system in which a touch responsive pulse is generated electromagnetically in response to key actuation. On the other hand, Kerkhof and Hammond employ capacitor discharge and charge facilities to provide a touch sensitive control voltage for a tone generator, allowing charge on a capacitor to vary for a time proportional to the time during which a key is in process of depression, so that the final charge retained by the capacitor is a direct function of the impact on the key.

In the prior art, the switch construction which controls timed capacitor discharge according to key velocity is complex, and therefore does not lend itself to economical production. In the present invention, a simple switch, composed of two spaced stationary contacts and one movable contact which moves from one to the other stationary contact on key actuation, in conjunction with a transfer valve, enables a voltage proportional to key velocity to be developed across a control capacitor and to be instantaneously transferred to a sustain capacitor in a tone gating circuit, without affecting the decay times of the capacitors at times subsequent to the transfer.

SUMMARY OF THE INVENTION In accordance with the invention, two parallel RC circuits are provided, one of which is a key depression timing or control circuit, and the other of which is a slow decay sustain circuit for a tone generator, such as an oscillator and gate. The timing or control circuit is connected to the movable arm of a single pole double throw switch, and the movable arm is normally connected to a stationary contact held to a relatively large voltage, so

3,516,321 Patented June 23, 1970 that the timing capacitor is normally maintained charged to that voltage. On actuating the key, contact is broken and the voltage across the timing capacitor proceeds to decay.

At lfinal key depression the movable arm arrives at the second contact, which is connected via a diode to the sustain circuit. Charge is now transferred from the capacitor of the timing circuit to the capacitor of the sustain circuit, 'via the diode. The timing circuit continues to decay rapidly, so that the diode becomes biased off as soon as it has transfered charge to the sustain capacitor, the latter being in a slow decay circuit. The sustain circuit then controls amplitude of a tone solely in accordance with its own decay characteristic, regardless of whether or not the key is maintained depressed. On release of the key the timing circuit re-attains its normal voltage substantially instantaneously.

As a further feature of the invention, the timing circuit is provided with a double rate of decay. The usual striking of a key may occupy from 5 ms. to 30 ms. in normal piano playing. Decay of voltage of the timing capacitor is permitted down to a preset minimum value, in 30 ms., but thereafter rate of decay is sharply reduced, so that total decay may require additional 250 ms. This provides a base value, so that some charge will be interchanged with the sustain capacitor regardless of how light the touch is. Thereby, the actual touch of a piano is more nearly simulated than is feasible with a single decay circuit, or than is feasible with an electromagnetic touch sensitive transducer, as in Markowitz. Decay time is then nearly hyperbolic, i.e. as l/t, instead of wholly exponential.

As a further feature of the invention, decay of the sustain capacitor has a double rate, initially rapid and terminally slow, to simulate the actual decay characteristic of piano strings.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects, features and attendant advantages of the present invention will become apparent from a consideration of the following detailed description of certain preferred embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a circuit diagram illustrated in simplified form of a basic feature of the invention, i.e. touch controlled switching and change transfer from a control to a sustain capacitor;

FIGS. 2 and 3 are circuit diagrams of modifications of the system of FIG. 1 providing for double rate decay of voltage across the control capacitor of FIG. 1;

FIG. 4 is a circuit diagram of a touch sensitive tone generating system employing features of FIG. 2;

FIG. 5 is a circuit diagram of a modification of the system of FIG. 4, including damping and percussion facilities;

FIG. 6 is a circuit diagram of a modification of the ssytem of FIG. 5, employing transistor transfer in place of diode transfer, and having novel damping facility;

FIG. 7 is a modification of the system of FIG. 6; and

FIGS. 8 and 9 are circuit diagrams of modifications of the systems of FIG. 7, having provisions for double rate decay of tone signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the accompanying drawings, FIG. 1 illustrates the basic approach of the invention. R1C1 is a timing circuit, connected between ground (at lead 10) and a negative voltage source V. One terminal of each of R1 and C1 is connected directly to lead 10 and the other terminal of each of R1 and C1 is connected to a 3 switch arm A, operable upward by the key 12 of a keyboard musical instrument. Switch arm A is normally in contact with switch contact B, which is in turn connected to source V. The voltage V therefore normally exists across C1.

On depressing key 12 contact between switch arm A and switch contact B is broken. The charge on capacitor C1 now commences to decay, in accordance with the values of RlCl, and these may be arranged to provide a drop from 50 v. to v., for example, in an elapsed time of 30 ms., which may be the time required to depress a piano key with a soft impact. The switch arm A, at the termination of key depression, makes with switch contact C, to which is connected, in cascade, the cathode of a diode and a timing circuit R2C2. The time constant of R202 is far greater than that of R1C1 so that once the transfer of charge is effective, and this occurs practically instantaneously, C2 is isolated from C1, because the cathode of diode 15 immediately becomes more positive than its anode. A square law relationship usually exists between output and velocity of key movement, i.e. output=kv. over a 30 db range with maximum sound level as a reference. Minimum travel time of a key may be taken to be about 5 milliseconds. Taking output at at 100, the relationship gives when x=3, i.e. 30 db down,

4 t= =30 ms.

Therefore, the timing circuit may be designed to fall to a low level in 30 ms. Values provided are exemplary of a typical action.

In order to produce a dynamic range similar to that of a piano it is necessary to allow the timing capacitor to discharge rapidly at first, i.e. out to 30 ms., and after the low level has been reached to decay much more slowly for about 2.50 ms. longer.

To achieve the double rate decay of timing voltage, two methods are employed, illustrated in FIGS. 2 and 3 of the accompanying drawings, and these may be briefly described as:

(1) switching a large capacitor into the timing circuit; (2) switching a small resistance out of the timing circuit.

In FIG. 2, capacitor C1 is normally maintained charged to the sum of V1 and B2, while contacts A and B make. Upon opening the circuit terminal of C1 proceeds to charge toward V1, along curve segment 21. Terminal 20 is connected via a diode D1 to the large capacitor C3, the cathode of diode D1 being biased from voltage divider VD to a point between 0 v. on lead 22 and V2 on lead 23. As point 20 rises in voltage from V2 toward +V1, a point is reached at which the diode D1 becomes conductive, whereupon C3 proceeds to charge, increasing the time constant to R1C1C3, and decreasing the rate of charging of C1, to follow the curve 24. The transition point 25 may be set at about -5 v., with V2 at about 50 v.

In FIG. 3, diode D2 is reversed, i.e. its cathode is connected to point 20, and its anode is connected to a small negative voltage V3 via a small resistance R3. The circuit can be analyzed by considering that current through R1 and R3 are of the same algebraic signs, so that net charging of C1 is fast via R1 and R3 in parallel, until diode D2 cuts off, i.e. point 20 becomes less nega- 4 tive than V3. After this point, 25, C1 charges only via R1, and therefore the rate is smaller, as at 24.

It is found that different time constants are required for white and black notes, because the distances between the striking points on the keys and the switches are different. Appropriate or exemplary circuit values for white and black keys are labeled W and B in the drawings, FIG. 4.

A practical circuit, including circuit values, capable of providing touch sensitive piano tones in a Baldwin Model 54 electric organ is provided in FIG. 4 of the accompanying drawings. The part of the figure to the left of line L has been heretofore explained in conjunction with FIG. 2 and therefore is not further explained. Circuit values are marked B and W, for black and white keys, respectively.

To the right of line L is shown the transfer diode D2, which at the time contacts A and C touch causes charge sharing between capacitors C1 and C2, as explained hereinabove, and thereafter isolation of C2 from C1 because time constant C1R1 is smaller than time constant C2R2. The voltage on C2 is led to diode gate 30, normally nonconductive, which leads tone signal from generator 31 to amplifier 32 and loudspeaker 33. This system produces a long decay output while the key K is held depressed, but release of the key does not change the action, i.e. no damping facility is present.

A piano provides tone damping action on key release. To provide damping action, the system of FIG. 5 is provided. FIG. 5 utilizes essentially the timing circuit of FIG. 3, which is not again explained. A neon cell N is provided, in shunt to diode D3. One terminal of N is connected through a resistance R4 to a switch point 35. A movable switch arm 36 serves to connect point 35 either to a v. terminal 37 or to a +11 v. terminal 38. The junction of R2 and C2 is also connected to an 11 v. lead via a diode D4, which prevents degradation of low level response by providing a clamp. The arm 36 is moved to the 80 v. terminal when damping is desired, and to the 11 v. terminal otherwise. In the latter case neon tube N remains always inoperative, but in the former case is fired when contacts AC separate and shunts diode D3 to provide a discharge path through R4 for C2, which parallels the normal path through R2, and leads to accelerated decay. Switch arm 36 is actuated by a socalled damping pedal, which has the function of preventing damping on key release.

With switch arm 36 in the undamped position, i.e. connected to +11 v., when A breaks with C the cathode of D3 moves to +11 v., which provides a voltage across N which is less than its striking voltage. C2 then discharges through R2 only.

With switch arm 36 in the damping position, i.e. connected to +80 v., when A breaks with C the cathode of D3 tries to move to +80 v., providing a voltage across N which is greater than its firing potential. N therefore fires, connecting R4 effectively in parallel with R2, thus increasing the discharge rate of C2.

Two supplementary switches S1 and S2 are provided, which switch operation of the system to produce selectively piano tone and organ type percussive tone. With S2 closed S1 is open, and vice versa. With S2 closed v. is applied to contact C1 as in FIG. 3.

When switch S2 is open and S1 closed, diode D5 provides a path to a 50 v. bus from an 11 v. bus via resistance R1. C1 is then charged normally to 50 v. This voltage is transferred to contact B when key K is actuated and is maintained so lOng as the key K is actuated. On release of the key K, action is similar to that for the piano mode. The percussion mode of operation is thus not touch sensitive, but starts all notes at the same level. Either a fast or slow decay may then be provided, according as switch S3 is in the one or the other of its operative conditions.

The disadvantages of the system of FIG. 5 are economic, i.e. one circuit is required for each note, and these circuits require large capacitors to provide adequate times.

In the system of FIG. 6, a timing capacitor C5 is normally maintained shorted by contacts B, A of a key controlled switch. Movable arm A of the switch is connected via a very large resistance R5 to a -12 v. bus 51, and via a diode D6 and a small resistance R6 to a -9 v. bus 51a. On separating arm A from contact B the capacitor C5 commences to charge toward -9 v. through resistance R6, until diode D6 cuts off. Thereafter, C5 charges toward -12 v. through R5. R6 may be 100K and R5 may be 100M, so that double rate decay occurs as in the system of FIG. 3. When arm A arrives at contact C, the voltage across C5 is applied to the base of transistor T1. The latter includes a collector, connected directly to v. bus 50, and an emitter, connected via a small resistance R6a to a capacitor C6, in series, to -12 v. bus 51. Transistor T1 has its base normally connected via a large resistance R7 to the bus 51, via contacts 55, for undamped operation. Transistor T1 is normally biased off, by the -12 v. applied to its base, but on completion of movement of key K a momentary voltage is applied between base and collector equal to that of the capacitor C5. Thereby a charge is applied to capacitor C6. The diode current of the base to emitter of T1 is now supplemented by collector-emitter current. The transistor T1 thus momentarily conducts just as arm A makes contact with point B, and then cuts off because its emitter is then biased positively with respect to its base.

The charge on C6 decays via R8 and via the base to emitter circuit of transistor T2, thereby varying the conductivity of T2.

Transistor T2 is connected in series with transistor T3 which acts as a gate, having its base directly connected to bus 50 and its emitter connected to a tone signal input terminal 53, which supplies tone by a series coupling capacitor C7 and resistance R8. Tone is taken off the collector of T3. Resistance R6a prevents DC thump during sampling, smoothing the charge of capacitor C6. Diode D8 assures that no negative charge can be assumed by capacitor C6, with respect to bus 51.

For damped operation contacts 56 are caused to close, so that on release of the key K, i.e. on separation of contacts A, C, 30' v. is applied to the base of T1 via R7. This is sufficient voltage to cause the base to emitter circuit of T1 to operate in its Zener region, discharging C6 through R7 down to -12 v., i.e. with a fast decay. So long as contacts A, C, make contact the base of T1 is caught by D7, at -12 v., preventing Zener breakdown.

The Zener breakdown characteristic of the base emitter diode of T1, when reverse biased, simulates the action of N in FIG. 5. With the damper switch connected to -30 v., and .A, C in contact, the base of T1 is maintained at -12 v. This does not provide Zener breakdown. When A breaks from C, i.e. when the key is released, the base of T1 falls towards -30 v., forcing the transistor into its Zener mode and effectively shunting R8 with R7 and increasing the discharge rate of C6. With the damper switch in the undamped position the reverse potential on the base emitter diode of T1 never approaches the Zener breakdown voltage, and when contact A breaks from contact C, C6 continues to discharge through R8 alone.

A diode D7 has its cathode connected to point 59 and its anode selectively to v. terminal 60 and to -12 v. terminal 61, selected by manually operated switch arm 62. With switch arm 62 up percussive action is attained, since point 59 cannot exceed 5 v., and for any normal key actuation 'will attain this value. Therefore in the percussive mode, appropriate to organ playing, 5 v. is applied to the base of T1 for each key actuation. For the piano mode point 59 cannot exceed -12 v., the same voltage as that of bus 51.

A modification of the system of FIG. 6 which has economic and operational advantages is illustrated in FIG. 7. The circuit of FIG. 7 does not utilize transistor gates or amplifiers, for producing tones, but instead the voltage appearing across a storage capacitor is applied to a diode gate, conventional per se.

The transistor T1 in FIG. 7, which also appears in FIG. 6, and which is identically controlled in FIG. 6 and FIG. 7, feeds current into an electrolytic capacitor C6a. That capacitor discharges into gate 65 via resistance R9.

A tone source terminal T is provided at an input to gate 65, which proceeds via a capacitor 66 to series diodes 67, 68, identically poled, and thence to a load L. A parallel RC shunt extends from the junction of diodes 67, 68 to ground. The impedance of shunt 70 is such that when the diodes 67 68 are rendered conductive by bias voltage applied to the anode of diode 67, a relatively high shunt is presented, in comparison with series impedance, and tone signal is not unduly attenuated. However, when the gate 60 is non-conductive the shunt impedance is low compared to the series impedance present, and feed through is radically reduced by being bypassed to ground.

The tone generator type applied to terminal T must be square wave shaped. Differentiation takes place at the circuits of diodes 67, 68, to present a signal containing essentially even harmonics. These are required to produce realistic piano tones. While the gate is non-conductive, a negative ofi-bias is produced in capacitor 66 to maintain the gate non-conductive in absence of positive on-gating voltage from capacitor C6a.

The system of FIG. 7 employs a single rate of decay. However, true piano tone decay exhibits two definite decay rates, the initial rate being greater than the terminal rate. Accordingly, the double rate decay expedient of FIG. 2 is applied to piano tone production in FIG. 8, i.e. discharge of sustain capacitor C6a occurs initially via small resistance R10 of about 39K, and large resistance R9 of 220K, until diode 10 cuts OE and thereafter only via R9. This system is level independent, i.e. the level at which the rate of decay decreases is independent of initial amplitude but is established by bias +2 on the diode D10.

In FIG. 9, two capacitors C20 and C21 are employed in parallel, as sustain capacitors. Values may be C20=1 and C21=10. R22 may have a value of 220K. R21 may have a value of K. In this circuit the terminal rate of decay is controlled by C20 and C21 in parallel discharging through R22. However, the initial charging pulse cannot charge C21 instantaneously, because of the presence of R21. Therefore, the initial condition is that C21 is initially uncharged or slightly charged, but C20 is fully charged. Discharge of C20 then occurs initially in part into C21 and in part through R22, and hence is rapid. Ultimately C21 becomes charged, and thereafter C20 and C21 discharge together through R22.

Various modifications of the present system will present themselves. For example, the oscillator and gate of FIG. 7, taken together, may be considered a tone source or generator. For such a generator may be substituted a tone oscillator, or the gate G may be a photoelectric gate, the tone source being a light modulator.

While I have disclosed a preferred embodiment of the invention, it will be apparent that variations in the specific details of construction which have been illustrated and described may be resorted to without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In a touch sensitive electronic musical instrument,

a diode having a Zener region when reverse biased,

a capacitor,

means including said diode for charging said capacitor, and

means for discharging said capacitor, said last means including means for reverse biasing said diode into its Zener region.

2. A system for generating a voltage proportional to the velocity with which a key of a musical instrument is impacted,

said key being movable by impact from a first to a second position, comprising means initiating a double rate decaying voltage wave at the instant of initial impact of said key,

means sampling the value of said voltage wave when said key attains said second position, and

means for storing the sampled value.

3. The combination according to claim 2 wherein said means for sampling includes a semiconductive unidirectional sampling valve.

4. The combination according to claim 2 wherein is provided a double rate decay circuit for said means for storing,

said double rate decay simulating the decay of string piano tone.

5. The combination according to claim 2 wherein is provided a decay circuit for said means for storing, the decay simulating decay of a percussive organ tone.

6. The combination according to claim 2, wherein is provided means for imparting to said voltage wave a peak amplitude which is a function of key velocity.

7. The combination according to claim 2 wherein is provided means for imparting to said voltage wave selectively a fixed peak amplitude on striking said key and a peak amplitude which is a function of key velocity on striking said key.

8. In an electronic-piano, a condenser charge and discharge circuit, including a single pole double throw switch, including a first contact movable between second and third stationary contacts,

a capacitor and a resistance connected in series with each other between a first bus and a second bus in the order stated,

means connecting said first contact to the junction of said capacitor and resistance,

means connecting said second contact to said first bus,

a source of voltage connected between said buses,

an electronic valve having an input terminal and an output terminal,

means connecting said third contact to said input terminal,

a storage capacitor connected to said output terminal,

and

key operated means for moving said first contact between said second and third stationary contacts.

9. In an electronic piano,

a key,

a control capacitor,

means normally maintaining said control capacitor charged to a predetermined level,

a resistive discharge circuit for said control capacitor,

means disabling said means for maintaining in response to an initial movement of said key, whereby said capacitor discharges continuously through said resistive discharge circuit for times following said initial movement,

means including a unidirectional electronic valve for only momentarily sampling the voltage of said capacitor during said discharge only at the instant of completion of a precisely predetermined movement of said key and for storing the voltage then momentarily sampled despite continuation of said discharge of said' control capacitor,

said last means including a storage capacitor for storing said momentarily sampled voltage,

a decay circuit normally connected across said storage capacitor,

a tone source, and

means for controlling the amplitude of the tone provided by said tone source as a function of the voltage of said storage capacitor,

wherein the slope of the decay curve of the voltage across said storage capacitor is smaller than the slope of the decay curve of the control capacitor, and

wherein said valve means includes a transistor arranged to transfer current to said storage capacitor in response to the voltage across said control capacitor.

10. In an electronic piano,

a key,

a control capacitor,

means normally maintaining said control capacitor charged to a predetermined level,

a resistive discharge circuit for said control capacitor,

means disabling said means for maintaining in response to an initial movement of said key, whereby said capacitor discharges continuously through said resistive discharge circuit for times following said initial movement.

means including a unidirectional electronic valve for only momentarily sampling the voltage of said capacitor during said discharge only at the instant of completion of a precisely predetermined movement of said key and for storing the voltage then momentarily sampled despite continuation of said discharge of said control capacitor,

said last means including a storage capacitor for storing said momentarily sampled voltage,

a decay circuit normally connected across said storage capacitor,

a tone source, and

means for controlling the amplitude of the tone provided by said tone source as a function of the voltage of said storage capacitor,

wherein the slope of the decay curve of the voltage across said storage capacitor is smaller than slope of the decay curve of the control capacitor, and

wherein said resistive discharge circuit includes means for imposing a double rate decay on the discharge of said control capacitor, said double rate decay including a relatively rapid rate of decay for approximately thirty milliseconds and a relatively slow rate of decay thereafter for about two hundred milliseconds.

11. In an electronic piano,

a key,

a control capacitor,

means normally maintaining said control capacitor charged to a predetermined level.

a resistive discharge circuit for said control capacitor,

means disabling said means for maintaining in response to an initial movement of said key, whereby said capacitor discharges continuously through said resistive discharge circuit for times following said initial movement,

means including a unidirectional electronic valve for only momentarily sampling the voltage of said capacitor during said discharge only at the instant of completion of a precisely predetermined movement of said key for storing the voltage then momentarily sampled despite continuation of said discharge of said control capacitor,

said last means including a storage capacitor for storing said momentarily sampled voltage,

a decay circuit normally connected across said storage capacitor,

a tone source, and

means for controlling the amplitude of the tone provided by said tone source as a function of the voltage of said storage capacitor,

wherein the slope of the decay curve of the voltage across said storage capacitor is smaller than slope of the decay curve of the control capacitor, and

wherein is provided means for at will accelerating decay of voltage of said storage capacitor, said last means including means for reverse biasing said electric valve means into a breakdown region of its operating characteristic.

12. The combination according to claim 6 wherein said 3,516,321 9 10 electric valve means 'nclud s a Zener breakdown re ion when reverse biased 1 e g HERMAN MRI. SAALBACH, Primary Examiner W. N. PUNTER, Assistant Examiner References C1ted UNITED STATES PATENTS 5 US. Cl. X.R.

2,482,548 9/1949 Kerkhof 84--1.26 841.21, 1.26, 1.27; 3201; 307-246, 293 3,248,470 4/ 1966 Markowitz 841.25 3,306,969 2/1967 Barber 84-124 

